Periscopic night sight having a filter disc for regulating the intensity of the input to a multistage image intensifier



@Ross May 6, 1969 w. H. sclDMoRE ET AL 6,443,105

PERISCOPIC NIGHT SIGHT HAVING A FILTER DISC FOR REGULATING THE INTENSITY OF THE INPUT TO A MULTISTAGE IMAGE INTENSFIER Filed March v, 196'/ 75 wwnfzmmf@ United States Patent Oce 3,443,105; Patented May 6, 1969 3,443,105 PERISCOPIC NIGHT SIGHT HAVING A .FILTER DISC FOR REGULATING THE INTENSITY OF THE INPUT TO A MULTISTGE- IMAGE INTENSIFIER .C `f- Wright H. Scidmore, Langhorne, and James W, Shean, Levittown, Pa., assignors to the Unitd' States of America as represented by the- Secretary'` of the Army Filed Mar. 7, 1967, Ser. No. 621,745 Int. Cl. H01j 39/12 U.S. Cl. 250--213 5 Claims ABSTRACT OF THE DISCLOSURE* -v A compact periscope having a high power night sighting capability and an unaided binocular day vision capability in which a manual-ly rotatable filter disc provides compensation for differing ambient levels of target illumination to permit use wit-h a high-gain multistage image intensifier.

This invention relates to optical instruments and more particularly concerns a compact periscopic optical instrument having high power night sighting capabilities coupled with means for unaided binocular day vision.

The inventive periscope described herein consists of two major assemblies, the head assembly andthe body assembly. The head assembly provides a laige'entrance aperture and the means for elevating and'depre'ssing the field of view. The body assembly houses a large'aperture optical system to pass as much of the availablelight as possible, an image intensifier tube, and opticalsystem to view the tube screen, a reticle projector systemto superimpose a ballistic reticle pattern on the tar-get' image, and a unity power optical system for direct dayvviewing.

The head assembly comprises a housing that contains two windows and an articulated head mirrorxThis articulated head mirror provides the means for an'fleS-degree depression and a ZZ-degree elevation of the`line-of-sight. The head mirror is moved by an internal mirror drive system, which is coupled lto the gun' trunnion by means of the parallelogram-type linkage. This shaft arid linkage arrangement insures that the periscop line-of-sight will be synchronized With the gun in elevation and depression.

The body assembly contains the catadioptric optical system which forms an image of the scene on the photocathode surface of the image intensifier tube and an optical system to view the tube screen. The optical system has nine power magnification andsix degrees field of view. A ballistic reticle pattern is projected into the catadioptric optical system of the b-ody by the ,reticle projector. Boresight adjustment is provided in the reticle projector.

The -optical systems of our inventive periscope comprise the unity power day system, the nine-power night system, and the optical system for the reticle projector. The head assembly contains elements common to the unity power and nine-power optical systems. `In the ninepower optical system, all light transmitting 'and reflecting elements with the exception of the elements used for recticle projection, and the elements of the image intensifier tube, are coated with high-efficiency reflection reducing or enhancing films, as appropriate, to increase the light transmission through the periscope. The coatings on the optical elements preceeding the' fiber optic `surface ofthe image intensifier tube are such as to be optimum over the spectral range of the photocathode surface.

The aforementioned provides a general description of our periscopic tank sight capable of use under low levels of illumination, the periscope being compact and yet usable with a 3stage image intensifier tube. Prior art telescopic tank sights providing night vision and unity power capabilities were, for the most part, usable only withfsingle stage intensifier tubes which were short in length and having a curved photocathode. The 3-stage image intensifier tube is about three times as long as its single stage counterpart, has a fiat cathode and is capable of much greater light amplification thus obviating any necessity of an active mode, such as a searchlight, for example, which may be readily detectable by the enemy. It is therefore a principal object of this invention to provide fan optical system having high power night sighting capability as well as unaided binocul-ar day vision capability. A i

Another object of this invention is t-o provide an optical system as aforementioned which is compact and yet usable with a 3-stage image intensifier tube. Still another object of the invention is to provide rl optical system having the advantages aforementioned which utilizes a concept yielding minimum obscuration (low T/No.). I?

The exact nature of this invention as well as other objectsjand advantages thereof will be readily apparent from consideration of the following description and drawings wherein: 'l

FIG. 1 illustrates a diagrammatic view of the optical system of our inventive periscope. I,

FIG. 2 illustrates another view of the optical syst m with components omitted for the sake of clarity.

Tjhe optical system depicted in the drawings includes a head assembly comprising an entrance window 10 through which light enters, is refiected from articulating head mirror 12 and transmitted through head assembly exit window 1'4 to the body assembly. Entrance window 10 is merely a plane parallel glass plate sealin-g the entrance aperture of the head assembly against the entry ofgdirt, moisture, or other foreign matter. The fully aluminized glass plate head mirror 12 provides a means for scanning the field of view in elevation through +2 degrees and -8 degrees.

Light rays passing through exit window 14 which contribute to the formation of an image for night observation are transmitted through window 1-6, outer areasgf corrector lenses 18 and 20, to primary objective mirror 22. Lens 20 has a 910 mirror-prism 2'4 cemented to underside. Primary mirror 22 folds the optical path of the light rays back 180 and converges the rays to form `an image, after being reflected on the hypotenuse surface of mirror-prism 24 and transmitted through filter disc 2'6, window 28 and field-flattener lens 30 at the light sensitive surface of 3-stage image intensifier tube 32. Corrector lens 18 and 20, in combination, serve as a means of balancing aberrations of the objective mirror and fieldattener lens. Both corrector lenses, in combination with the objective mirror 90 mirror-prism, filter disc, window and field-flattener lens comprise the catadioptric objective optical-system.

A/Filter disc 26 is a plane parallel glass plate with four oblong apertures 26' having degrees of coatings varying from clear to near opaque for regulating the light falling on the photocathode surface ofthe intensifier tube. Reticle light will be transmitted through smaller complementary filter apertures 26 to maintain a constant ratio of intensity of the reticle pattern with respect to the target image at the photocathode surface of the image intensifier tube.

Rays from the visible image formed on the screen of the image intensifier tube are transmitted through a field-flattener lens 314, 90 prism 36, collective lens 38, Amici prism 40, and are collimated by first erector lenses 42 and 44. The rays are then focused at the eyepiece focal plane by second erector lenses 46 and 48 and focused at infinity by the eyepiece which consists of field lenses 50 and 52 having a diaphragm 53 thereinbetween and serving as a field stop, center lens 54 and eye lens 56. Plus or minus 4 diopters adjustment is provided by longitudinal adjustment of the second erector lenses.

Light rays contributing to the unit power field are transmitted through window 16, the central portions of corrector lenses 18 and 20, are deviated 90 by (1) mirror surface of mirror-prism 24, (2) mirror 60 and (3) mirror 62 for transmittal through window `64 to the observers eyes. Window 64 is a weak negative lens of approximately 1/2 diopter thereby requiring a small, desirable amount of eye accommodation when using the unit power vision system.

Light from reticle 70 (illuminated by a reticle lamp, not shown) is collimated by lens 72, is transmitted through an aperture 26 in filter 26, and deviated 90 by prism 74, resting atop pedestal 75, into converging lens 76. Lens 76 converges the light to a focus at the light sensitive surface of 3-stage image intensifier tube after being deviated 90 along the optical axis of the system by the mirror of mirror-prism 24 and transmitted through filter 26window 28, and field-flattener lens 30. Lens 76, which is identical to lens 72, has a plane surface to permit cernenting of this element to prism 74.

Filter disc 26 is manually rotatable and provides cornpensation for differing ambient levels of illumination of the target seen. lFor example, under full moon conditions, the opacity of oblong apertures of 26 of filter 26 will be greater than under, lets say, starlight conditions.

Mirror-prism 24 not only reflects the target, seen through window 64 after being reflected from mirrors 60 and 62 for binocular observation at unity power but also reflects energy from primary mirror 22 of the night system through the filter and into the image intensifier tube. It should be borne in mind that our invention periscope includes no movable component for unaided binocular day vision.

Reference is hereby made to patent application, Ser. No. 621,744 of Wright H. Scidmore and Ezra Weitzel for Catadioptric System for Night `Periscopic Sight, filed Mar. 7, 1967, assigned to the same assignee of this patent application.

We claim:

1. A compact periscope having a high power night sighting capability for use under extremely low levels of illumination and an unaided binocular day vision capability comprising:

a periscope head assembly for receiving light rays devoid of any active mode from object space,

a periscope body for receiving said rays transmitted through said head assembly, said body including a high power night channel comprising a body window,

an upper corrector lens and a lower corrector lens after said body window and axially aligned therewith,

a 90 mirror-prism having a reflective hypotenuse surface, said mirror-prism being cemented to a entral underportion of said lower corrector ens,

a primary mirror below said mirror-prism for refleeting light rays passing through outer portions of both of said corrector lenses onto said hypotenuse surface of said mirror-prism,

a manually rotatable filter disc for lfiltering said rays reflected from said hypotenuse surface for transmission into a multi-stage image intensifier tube to form a target image,

means for projecting a reticle pattern into said intensifier tube for superimposition thereof on said target image, and

additional means for visually observing said images.

2. The device of claim 1 further characterized by said means for projecting a reticle pattern into said image intensifier tube for superimposition on said target image comprising:

a source of light energy,

a reticle for receiving said light energy,

a lensl for collimating said light energy after passing through tsaid reticle,

a prism for deviating said collimated light energy,

a converging lens for converging said deviated light to a focus at a light-sensitive surface of said multistage image intensifier tube.

3. The device of. claim 1 further characterized by said periscope bodyincluding an unaided binocular day vision capability wherein said '90 mirror-prism reflects light rays passing,through a central portion of both of said correctory lenses.onto a pair of reflecting mirrors through a window, saidbinoular day vision capability being devoid of any moving parts.

4. The deyicefofpclaim 1 wherein said filter disc is a plane parallel glassplate having a plurality of oblongshaped filter patches, each of said patches having a different degree of opacity ranging from clear to near opaque, said -filterdisc including a plurality of complementary filter apertures for permitting reticle light to pass therethrough for maintaining a constant ratio of intensity of reticle pattern with respect to said target image at a photocathode surface of said multistage image intensifier tube.

5. Incombination with a multi-stage intensifier tube, a compact periscope having a high power night sighting capability for use under extremely low levels of illumination and an unaided binocular day vision capability comprising:

a periscope head assembly for receiving light rays devoid of any active mode from object space,

a periscope body for receiving said rays transmitted through said head assembly, said body including a high power night channel comprising a body window,

an upper c'or'rector lens and a lower corrector lens afterl said body window and axially aligned therewith,

a 90 mirror-prism having a reflective hypotenuse surface, said mirror-prism being cemented to a central underportion of said lower corrector lens,

a primary mirror below said mirror-prism for reflecting light rays passing through outer portions of both of said corrector lenses onto said hypotenuse surface of said mirror-prism,

a manually rotatable filter disc for filtering said rays reflected from said hypotenuse surface for transmission into said multi-stage image intensifier tube to form a target image,

means for projecting a reticle pattern into said intensifier tube for superimposition thereof on said target image, and

additional means for visually observing said images..

References Cited UNITED STATES PATENTS 3,324,300 6/1967 Bouwers 250-213 3,200,250 8/1965 Bouwers 250-213 X 3,257,904 6/1966 Scidmore et al. 350-202 3,155,832 l1/l964 Bouwers 250-213 RALPH G. NILSON, Primary Examiner.

T. N. GRIGSBY, Assistant Examiner.

Us. c1. x. R. 350g-199, 202 

